/*
 * Copyright (C) 2008, Google Inc.
 * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
 * Copyright (C) 2006-2012, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.glodon.paas.document.storage.id;

import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/** Misc. constants used throughout JGit. */
public final class Constants {
    /** Hash function used natively by Git for all objects. */
    private static final String HASH_FUNCTION = "SHA-1";

    /**
     * A Git object hash is 160 bits, i.e. 20 bytes.
     * <p>
     * Changing this assumption is not going to be as easy as changing this
     * declaration.
     */
    public static final int OBJECT_ID_LENGTH = 20;

    /**
     * A Git object can be expressed as a 40 character string of hexadecimal
     * digits.
     *
     * @see #OBJECT_ID_LENGTH
     */
    public static final int OBJECT_ID_STRING_LENGTH = OBJECT_ID_LENGTH * 2;

    /** Special name for the "HEAD" symbolic-ref. */
    public static final String HEAD = "HEAD";

    /** Special name for the "FETCH_HEAD" symbolic-ref. */
    public static final String FETCH_HEAD = "FETCH_HEAD";

    /**
     * Text string that identifies an object as a commit.
     * <p>
     * Commits connect trees into a string of project histories, where each
     * commit is an assertion that the best way to continue is to use this other
     * tree (set of files).
     */
    public static final String TYPE_COMMIT = "commit";

    /**
     * Text string that identifies an object as a blob.
     * <p>
     * Blobs store whole file revisions. They are used for any user file, as
     * well as for symlinks. Blobs form the bulk of any project's storage space.
     */
    public static final String TYPE_BLOB = "blob";

    /**
     * Text string that identifies an object as a tree.
     * <p>
     * Trees attach object ids (hashes) to names and file modes. The normal use
     * for a tree is to store a version of a directory and its contents.
     */
    public static final String TYPE_TREE = "tree";

    /**
     * Text string that identifies an object as an annotated tag.
     * <p>
     * Annotated tags store a pointer to any other object, and an additional
     * message. It is most commonly used to record a stable release of the
     * project.
     */
    public static final String TYPE_TAG = "tag";

    private static final byte[] ENCODED_TYPE_COMMIT = encodeASCII(TYPE_COMMIT);

    private static final byte[] ENCODED_TYPE_BLOB = encodeASCII(TYPE_BLOB);

    private static final byte[] ENCODED_TYPE_TREE = encodeASCII(TYPE_TREE);

    private static final byte[] ENCODED_TYPE_TAG = encodeASCII(TYPE_TAG);

    /** An unknown or invalid object type code. */
    public static final int OBJ_BAD = -1;

    /**
     * In-pack object type: extended types.
     * <p>
     * This header code is reserved for future expansion. It is currently
     * undefined/unsupported.
     */
    public static final int OBJ_EXT = 0;

    /**
     * In-pack object type: commit.
     * <p>
     * Indicates the associated object is a commit.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     *
     * @see #TYPE_COMMIT
     */
    public static final int OBJ_COMMIT = 1;

    /**
     * In-pack object type: tree.
     * <p>
     * Indicates the associated object is a tree.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     *
     * @see #TYPE_BLOB
     */
    public static final int OBJ_TREE = 2;

    /**
     * In-pack object type: blob.
     * <p>
     * Indicates the associated object is a blob.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     *
     * @see #TYPE_BLOB
     */
    public static final int OBJ_BLOB = 3;

    /**
     * In-pack object type: annotated tag.
     * <p>
     * Indicates the associated object is an annotated tag.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     *
     * @see #TYPE_TAG
     */
    public static final int OBJ_TAG = 4;

    /** In-pack object type: reserved for future use. */
    public static final int OBJ_TYPE_5 = 5;

    /**
     * In-pack object type: offset delta
     * <p>
     * Objects stored with this type actually have a different type which must
     * be obtained from their delta base object. Delta objects store only the
     * changes needed to apply to the base object in order to recover the
     * original object.
     * <p>
     * An offset delta uses a negative offset from the start of this object to
     * refer to its delta base. The base object must exist in this packfile
     * (even in the case of a thin pack).
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     */
    public static final int OBJ_OFS_DELTA = 6;

    /**
     * In-pack object type: reference delta
     * <p>
     * Objects stored with this type actually have a different type which must
     * be obtained from their delta base object. Delta objects store only the
     * changes needed to apply to the base object in order to recover the
     * original object.
     * <p>
     * A reference delta uses a full object id (hash) to reference the delta
     * base. The base object is allowed to be omitted from the packfile, but
     * only in the case of a thin pack being transferred over the network.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     */
    public static final int OBJ_REF_DELTA = 7;

    /**
     * Pack file signature that occurs at file header - identifies file as Git
     * packfile formatted.
     * <p>
     * <b>This constant is fixed and is defined by the Git packfile format.</b>
     */
    public static final byte[] PACK_SIGNATURE = { 'P', 'A', 'C', 'K' };

    /** Native character encoding for commit messages, file names... */
    public static final String CHARACTER_ENCODING = "UTF-8";

    /** Native character encoding for commit messages, file names... */
    public static final Charset CHARSET;

    /** Default main branch name */
    public static final String MASTER = "master";

    /** Default stash branch name */
    public static final String STASH = "stash";

    /** Prefix for branch refs */
    public static final String R_HEADS = "refs/heads/";

    /** Prefix for remotes refs */
    public static final String R_REMOTES = "refs/remotes/";

    /** Prefix for tag refs */
    public static final String R_TAGS = "refs/tags/";

    /** Prefix for notes refs */
    public static final String R_NOTES = "refs/notes/";

    /** Standard notes ref */
    public static final String R_NOTES_COMMITS = R_NOTES + "commits";

    /** Prefix for any ref */
    public static final String R_REFS = "refs/";

    /** Standard stash ref */
    public static final String R_STASH = R_REFS + STASH;

    /** Logs folder name */
    public static final String LOGS = "logs";

    /** Info refs folder */
    public static final String INFO_REFS = "info/refs";

    /** Packed refs file */
    public static final String PACKED_REFS = "packed-refs";

    /** The environment variable that contains the system user name */
    public static final String OS_USER_NAME_KEY = "user.name";

    /** The environment variable that contains the author's name */
    public static final String GIT_AUTHOR_NAME_KEY = "GIT_AUTHOR_NAME";

    /** The environment variable that contains the author's email */
    public static final String GIT_AUTHOR_EMAIL_KEY = "GIT_AUTHOR_EMAIL";

    /** The environment variable that contains the commiter's name */
    public static final String GIT_COMMITTER_NAME_KEY = "GIT_COMMITTER_NAME";

    /** The environment variable that contains the commiter's email */
    public static final String GIT_COMMITTER_EMAIL_KEY = "GIT_COMMITTER_EMAIL";

    /**
     * The environment variable that limits how close to the root of the file
     * systems JGit will traverse when looking for a repository root.
     */
    public static final String GIT_CEILING_DIRECTORIES_KEY = "GIT_CEILING_DIRECTORIES";

    /**
     * The environment variable that tells us which directory is the ".git"
     * directory
     */
    public static final String GIT_DIR_KEY = "GIT_DIR";

    /**
     * The environment variable that tells us which directory is the working
     * directory.
     */
    public static final String GIT_WORK_TREE_KEY = "GIT_WORK_TREE";

    /**
     * The environment variable that tells us which file holds the Git index.
     */
    public static final String GIT_INDEX_FILE_KEY = "GIT_INDEX_FILE";

    /**
     * The environment variable that tells us where objects are stored
     */
    public static final String GIT_OBJECT_DIRECTORY_KEY = "GIT_OBJECT_DIRECTORY";

    /**
     * The environment variable that tells us where to look for objects, besides
     * the default objects directory.
     */
    public static final String GIT_ALTERNATE_OBJECT_DIRECTORIES_KEY = "GIT_ALTERNATE_OBJECT_DIRECTORIES";

    /** Default value for the user name if no other information is available */
    public static final String UNKNOWN_USER_DEFAULT = "unknown-user";

    /** Beginning of the common "Signed-off-by: " commit message line */
    public static final String SIGNED_OFF_BY_TAG = "Signed-off-by: ";

    /** A gitignore file name */
    public static final String GITIGNORE_FILENAME = ".gitignore";

    /** Default remote name used by clone, push and fetch operations */
    public static final String DEFAULT_REMOTE_NAME = "origin";

    /** Default name for the Git repository directory */
    public static final String DOT_GIT = ".git";

    /** Default name for the Git repository configuration */
    public static final String CONFIG = "config";

    /** A bare repository typically ends with this string */
    public static final String DOT_GIT_EXT = ".git";

    /** Name of the ignore file */
    public static final String DOT_GIT_IGNORE = ".gitignore";

    /** Name of the submodules file */
    public static final String DOT_GIT_MODULES = ".gitmodules";

    /** Name of the .git/shallow file */
    public static final String SHALLOW = "shallow";

    /**
     * Create a new digest function for objects.
     *
     * @return a new digest object.
     * @throws RuntimeException
     *             this Java virtual machine does not support the required hash
     *             function. Very unlikely given that JGit uses a hash function
     *             that is in the Java reference specification.
     */
    public static MessageDigest newMessageDigest() {
        try {
            return MessageDigest.getInstance(HASH_FUNCTION);
        } catch (NoSuchAlgorithmException nsae) {
            throw new RuntimeException(nsae);
        }
    }

    /**
     * Convert an OBJ_* type constant to a TYPE_* type constant.
     *
     * @param typeCode the type code, from a pack representation.
     * @return the canonical string name of this type.
     */
    public static String typeString(final int typeCode) {
        switch (typeCode) {
        case OBJ_COMMIT:
            return TYPE_COMMIT;
        case OBJ_TREE:
            return TYPE_TREE;
        case OBJ_BLOB:
            return TYPE_BLOB;
        case OBJ_TAG:
            return TYPE_TAG;
        default:
            throw new IllegalArgumentException();
        }
    }

    /**
     * Convert an OBJ_* type constant to an ASCII encoded string constant.
     * <p>
     * The ASCII encoded string is often the canonical representation of
     * the type within a loose object header, or within a tag header.
     *
     * @param typeCode the type code, from a pack representation.
     * @return the canonical ASCII encoded name of this type.
     */
    public static byte[] encodedTypeString(final int typeCode) {
        switch (typeCode) {
        case OBJ_COMMIT:
            return ENCODED_TYPE_COMMIT;
        case OBJ_TREE:
            return ENCODED_TYPE_TREE;
        case OBJ_BLOB:
            return ENCODED_TYPE_BLOB;
        case OBJ_TAG:
            return ENCODED_TYPE_TAG;
        default:
            throw new IllegalArgumentException();
        }
    }

    /**
     * Convert an integer into its decimal representation.
     *
     * @param s
     *            the integer to convert.
     * @return a decimal representation of the input integer. The returned array
     *         is the smallest array that will hold the value.
     */
    public static byte[] encodeASCII(final long s) {
        return encodeASCII(Long.toString(s));
    }

    /**
     * Convert a string to US-ASCII encoding.
     *
     * @param s
     *            the string to convert. Must not contain any characters over
     *            127 (outside of 7-bit ASCII).
     * @return a byte array of the same length as the input string, holding the
     *         same characters, in the same order.
     * @throws IllegalArgumentException
     *             the input string contains one or more characters outside of
     *             the 7-bit ASCII character space.
     */
    public static byte[] encodeASCII(final String s) {
        final byte[] r = new byte[s.length()];
        for (int k = r.length - 1; k >= 0; k--) {
            final char c = s.charAt(k);
            if (c > 127)
                throw new IllegalArgumentException();
            r[k] = (byte) c;
        }
        return r;
    }

    /**
     * Convert a string to a byte array in the standard character encoding.
     *
     * @param str
     *            the string to convert. May contain any Unicode characters.
     * @return a byte array representing the requested string, encoded using the
     *         default character encoding (UTF-8).
     * @see #CHARACTER_ENCODING
     */
    public static byte[] encode(final String str) {
        final ByteBuffer bb = Constants.CHARSET.encode(str);
        final int len = bb.limit();
        if (bb.hasArray() && bb.arrayOffset() == 0) {
            final byte[] arr = bb.array();
            if (arr.length == len)
                return arr;
        }

        final byte[] arr = new byte[len];
        bb.get(arr);
        return arr;
    }

    static {
        if (OBJECT_ID_LENGTH != newMessageDigest().getDigestLength())
            throw new LinkageError();
        CHARSET = Charset.forName(CHARACTER_ENCODING);
    }

    /** name of the file containing the commit msg for a merge commit */
    public static final String MERGE_MSG = "MERGE_MSG";

    /** name of the file containing the IDs of the parents of a merge commit */
    public static final String MERGE_HEAD = "MERGE_HEAD";

    /** name of the file containing the ID of a cherry pick commit in case of conflicts */
    public static final String CHERRY_PICK_HEAD = "CHERRY_PICK_HEAD";

    /** name of the file containing the commit msg for a squash commit */
    public static final String SQUASH_MSG = "SQUASH_MSG";

    /**
     * name of the ref ORIG_HEAD used by certain commands to store the original
     * value of HEAD
     */
    public static final String ORIG_HEAD = "ORIG_HEAD";

    /** objectid for the empty blob */
    public static final ObjectId EMPTY_BLOB_ID = ObjectId.fromString("e69de29bb2d1d6434b8b29ae775ad8c2e48c5391");

    private Constants() {
        // Hide the default constructor
    }
}
